Solar power generation systems that concentrate sunlight using a lens, a reflective plate, or the like, and generate power using heat collected in the area of the concentrated sunlight are beginning to play a more significant role. FIG. 6 illustrates an example of a solar power generation system introduced in Non-Patent Document 1 described below. The solar power generation system illustrated in FIG. 6 is an example of a so-called tower-type based system and, within the tower-type subgroup, a so-called direct steam generation (DSG) based system. A system 100 illustrated in FIG. 6 includes a reflector group 102 configured by a collection of a plurality of reflectors called heliostats that reflect sunlight toward an upper portion of a tower 104, a collector 106 that is provided to the upper portion of the tower 104, is heated by the sunlight reflected by the reflector group 102, and produces steam from fed water, a water feeder 108 that feeds water to the collector 106, a power generating portion 110 that generates power by the steam produced by the collector 106 and fed thereto, and a condenser 112 that condenses the steam used for power generation in the power generating portion 110, and feeds the water produced by condensation once again to the water feeder 108.
The collector 106 is a container-like member, and includes a plurality of heat storage bodies described later having a relatively large heat capacity. The thermal energy of the sunlight collected in the collector 106 by the reflector group 102 is stored in these heat storage bodies. The water fed from the water feeder 108 to the collector 106 is heated by the thermal energy of these heat storage bodies and turned into steam. This steam is fed to the power generating portion 110, and rotates, for example, a power generation turbine (not illustrated) provided in the power generating portion 110 to generate power.
Such a solar power generation system converts thermal energy stored in the heat storage bodies into electrical energy, and therefore offers advantages such as the ability to continually generate power even at nighttime when sunlight is not directly irradiated, using the stored thermal energy. To store a large amount of thermal energy, heat storage bodies, each having a relatively large heat capacity, need to be disposed in the collector 106 as many as possible (that is, at high density).
The heat storage bodies each include a heat storage material having a relatively large heat capacity, and a container that houses this heat storage material. As the heat storage material, salt (NaCl) which is inexpensive and has a large heat capacity is often used. While the melting point of salt is a high 800° C., the heat storage in a solar power generation system is heated to a temperature that significantly exceeds this 800° C.
FIG. 7 is a cross-sectional view for explaining an embodiment of a conventional heat storage described in Patent Document 1 described below. A heat storage 200 includes a cylindrical member 202 having a bottomed cylindrical shape, a lid 204, and a heat storage material 210 disposed in the interior of the cylindrical member 202. An opening end 202a of the cylindrical member 202 is blocked by the welding of the tubular 202 and the lid 204.